1. Field of the Invention
The present invention relates to a film winding system of a camera.
2. Description of the Related Art
Conventionally, there are popularized cameras having a film winding mechanism with a motor In such types of the cameras, especially, having an automatic film winding mechanism, the film winding mechanism is driven and turned off with the motor integrated in the camera, repeatedly and with high frequency, so that reliability and durability of the film winding mechanism may be important. Specially, a winding stopper device, for example, a lock mechanism for the film winding mechanism, for stopping the operation of the film winding mechanism with accuracy has important influence on the reliability and the durability of the film winding mechanism.
In the case where the film winding mechanism which is driven with a predetermined driving force is forced to stop with the lock mechanism after the motor is turned off, both of the film winding mechanism and the lock mechanism come into tension by means of inertia of rotating members since the rotating members such as gears and shafts which are comprised of a reduction gear system for a power transmission of the film winding mechanism have a rotational inertia. If such a condition is caused frequently in the film winding mechanism, it has bad influence on the durability of the film winding mechanism. In addition, a required force for dis-locking a lock member of the lock mechanism out of the film winding mechanism becomes much. Even in the case of a camera having a motor braking system, the problem is not completely solved.
As described above, in the camera having such an automatic film winding mechanism, a relatively heavy load acts on the winding stopper device at completion of the film winding, so that dis-locking of the stopper device requires a large amount of a counter force against the load on the occasion of the successive film winding. There are various types of structures of dis-locking mechanisms available, corresponding to the types of stopper devices. No matter what type of the dis-locking mechanisms is, the automatic film winding mechanism normally has a driving source for dis-locking the stopper device. For example, in the case of an automatic film winding mechanism having a stopper device including a lock lever which is actuated by a spring and by which the stopper device is dis-locked, the mechanism requires holding means (driving source) for holding an operating position of the lock lever by which the mechanism is locked against the spring force. If a magnet unit, for example, as such holding means, may be utilized, a size of the magnet unit which is accommodated in a camera body is limited fundamentally. Accordingly, a dynamic power to be generated by the magnet is limited, so that the spring force capable of holding the lock lever at its non-operating position by the spring is limited.
A driving capacity of the driving source should exceeds, at least, the spring force (dis-locking force). On the other hand, it is preferable that the driving source in the camera body is a smaller one as much as possible from the miniaturized point of view on a camera. Therefore, it is one factor and is very important for miniaturization and cost-down of a camera that the dis-locking of the stopper device is enabled by a smaller dynamic power. Furthermore, if it is enabled to dis-lock the stopper device with the smaller dynamic power, it is ensured to dis-lock the automatic film winding mechanism. As a result of that, it is improved that reliability of the automatic film winding mechanism.
As described above, to accomplish an improvement of the reliability of the film winding mechanism, countermeasures to be taken are as follows and effective.
That is, one is to reduce the dynamic force acting on the winding stopper device as much as possible. The dynamic force necessary for releasing the film winding mechanism from the locked state of that can be reduced if the load acting on the lock mechanism for restraining the film winding by the film winding mechanism is loosed in advance before initiation of a subsequent film winding to a preceding one.
The other is to create more opportunity to dis-lock and/or release the stopper device for a short period as much as possible. In the case where the dis-locking does not work due to something wrong, for example, in the case where the dis-locking does not work since the reduction gear system of the film winding system is out of order, the camera is out of order, as well. In the conventional cameras, normally, the opportunity for releasing a locked state of the film winding mechanism is one time, so that a function of the camera stops at the locked state of that if the above-mentioned releasing does not effected due to the above-mentioned trouble. Therefore, increasing of the opportunity as a one countermeasure is necessary. Meanwhile, if the camera is out of order due to the trouble relating to other factors, for example, non-detection of the releasing of the film winding mechanism nevertheless the releasing is effected, it is preferable for the camera that its operation system return to its initial stage.
Meanwhile, most of conventional cameras having a film winding mechanism for winding a film roll with one motor integrated therein are a type (so-called winder type) of camera which performs set-cocking of a spring adapted for a quick-return of a mirror and shutter-cocking in parallel with the film winding. On one hand, there is provided a camera having a function capable of performing a processing of a shutter release with a motor and capable of winding the film roll with a reversible direction of the same motor. In these types of cameras, the film roll is fed by a film sprocket and is wound by a spool. Accordingly, a friction mechanism for absorbing a difference of a peripheral speed between the sprocket and the spool is interposed therebetween. And it is so designed that the friction mechanism works always in operation of the film winding. In the camera, a lock mechanism for indexing a feeding amount of the film roll by the sprocket and locking a film winding mechanism is provided, and it is so arranged that the lock mechanism is dis-locked during a release process or at a return of a diaphragm and mirror. Accordingly, in order to wind the film roll, it is always necessary to carry out the release process. Therefore, a releasing operation is requested additionally nevertheless just a feeding operation of the film roll is requested in this case, similarly to an initial load process of the camera, so that an electric power is wasted and it takes a lot of times. In addition to the above, in the case of completion of photographing, a film winding process is always transferred at completion of the release process, so that it causes waste of time.
Recently, there are provided cameras which have a function that a film roll is directly wound around the spool by itself. Advantages of this type of cameras is to eliminate the above-mentioned friction mechanism. Therefore, there are disadvantages described above, and there is a merit that a time necessary for the film winding can be reduced. On the contrary to the above, there is a disadvantage in this camera that it is difficult to carry out the film winding operation in parallel with the shutter cocking operation through one motor since a rotational amount of the spool changes depending on a wound film therearound is and is not constant. The mechanism of the spool winding-type carry out the cocking process through the film. Accordingly, there is no problem for a lens shutter-type camera in which the cocking operation is carried out by a driven sprocket but that mechanism can not be applied to a single-reflex camera since a focal plain shutter requires a large amount of dynamic force. There are further disadvantages as follows. Namely, there is possibility that that a light leakage during a film rewinding operation is caused since the shutter cocking is not completed at sticking the film, and that the shutter is wounded by a film lip during an initial resetting operation after completion of the film rewinding operation.
On the other hand, if the cocking is completed before initiation of the film winding operation, it may be enabled that the releasing operation is initiated before completion of the film winding operation, so that it may be possible to increase a feeding speed of the film roll. In addition, in this case, there are an advantage that only the cocking operation is requested on the occasion of a multiexposure and completion of photographing. Under the circumstances, it is desirable that the cocking system and the film winding system are driven independently from each other, resulting in that most of recent camera have two motors and each system has own motor. It is called "a two motors driving system".
Meanwhile, each driving characteristic of the cocking system and the film winding system is different from each other. A load for winding the film roll varies at a low temperature, so that the operations of the cocking process may be fulfilled under one driving characteristic of the driving motor if the operations of the film winding process may not be fulfilled due to a lack of the motor power under that driving characteristic of the motor, for example, under a high rotational speed with low torque. On the contrary to the above, if the temperature rises, the operations of the film winding process may be fulfilled under that driving characteristic although the operations of the cocking process can be not fulfilled under that characteristic. Accordingly, it is preferable that the two systems are driven individually. An additional advantage of the two motors driving system is that the motor driving can be shifted through a reduction system depending on a current load which acts on the driven system, so that it contributes to a high speed operation of the camera.
For example, a camera which has been disclosed by (Japan Patent Laid-open Publication No. 62-8937(1987) has two motors and two transmission systems having different reduction ratios per one motor. The camera is so designed that shifting to a low speed side of each system is fulfilled at the same time when an extremely low speed of the film winding is detected by detecting means of the film feeding speed. As an another example of a conventional camera, speed detection means for detecting a film feeding speed is provided in each of the cocking system and the film winding system, and it is so designed that both systems are driven under a low speed driving mode shifted from a high speed driving mode when one of the speed detection means detects an extremely low speed of the film feed. In these examples, the driving mode of the two systems is shifted to the low speed side at the same time when the abnormal on the film feeding speed is detected, so that each of the systems is not always driven under a proper driving characteristic which meets with a current one required by the system. Accordingly, a driving efficiency of each of the systems does not always become high. That is one of the disadvantages to such a type of the conventional cameras. Further, a lot of devices such as two motors, four transmission systems in total, and so on, is required and a space in which these devices are accommodated is required in a camera body, so that it does not contributes to miniaturization and cost-down of a camera. This is another disadvantage to the conventional type camera.
As previously described, in order to accomplish the multi-exposure, the two motors driving system is more convenient because the cocking system can be only driven easily. However, one of disadvantages in this system, as aforementioned, is that a structure of the film winding mechanism and the cocking mechanism of the diaphragm, the shutter, and mirror becomes complicated. Further disadvantages are costly and a spacing problem in the camera body. The best way for accomplishing the multi-exposure must be to be fulfilled by a simple structure of the driving mechanism, as well as, by a simple operation for the multi-exposure photographing.